Road marker (4)
'road marker' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cone that I've seen before include "Circular pyramid" , "Tapering object" , "Tapering shape" , "Shape, the base is a circle and the sides taper up to a point" , "Volcano peak" .)
(Other definitions for pylon that I've seen before include "Steel structure carrying cables" , "Electric cable tower" , "It marks turning point in a race" , "Tower supporting power lines" , "Electricity cable support" .)